An organic light emitting diode (OLED) device is a self-luminescence device, and has ascendancies such as low operating voltage, wide viewing angle, fast response and temperature adaptability, so that the OLED device is a new generation of display technique. Recently, the OLED panel has been fabricated with a commercial yield by few manufacturers, and some companies also enter R&D and commercial yield phases of the OLED device.
The luminescence principle of the OLED device is that holes and electrons are respectively injected from anode and cathode; then the holes pass through hole injection and transport layer electron injection layer, the electrons pass through electron injection and transport layer; then combination of the holes and the electrons provides energy to form excitons in light emitting layer; and the excitons radiate luminescence due to attenuation from excited state to bound state of exciting electrons of the excitons.
A key point of enhancing efficiency and lifetime of the OLED device is equilibrium between a hole-concentration current and an electron-concentration current in a light emitting layer of OLED device. However, an electron mobility of a conventional electron-transporting material is about 10−5 cm2v−1s−1-10−6 cm2v−1s−1, a hole mobility of a conventional hole-transporting material is about 10−2 cm2v−1s−1-10−3 cm2v−1s−1, and the hole mobility of the conventional hole-transporting material is about 1000 times of the electron mobility of the conventional electron-transporting material, so that a difference between the hole mobility and the electron mobility thereof causes un-equilibrium of the hole-concentration current and the electron-concentration current in the light emitting layer of OLED device. The un-equilibrium between the hole-concentration current and the electron-concentration current allows the combination zone of the holes and electrons be formed nearby cathode, and produces excess hole-concentration current to quench the excitons formed in the light emitting layer, so as to decrease the efficiency and lifetime of the OLED device. For the aspect of enhancing the efficiency and lifetime of the OLED device, an electron-transporting material has need to meet demands of higher electron mobility, higher electron affinity, and stronger electron-accepting and electron-transporting ability.
Another key point of enhancing efficiency and lifetime of OLED device is that the combination zone of the holes and the electrons can be set in the entire light emitting layer, accordingly, a host material of radiating phosphorescence for electroluminescence devices shall be a dipole material having both high hole and electron mobility. Most of currently available materials of radiating phosphorescence are not a dipole material (i.e. have not both high hole and electron mobility), a great difference between the hole and the electron mobility thereof allows the combination zone of the holes and electrons be formed nearby one side of the OLED device (e.g. cathode), but not in the entire light emitting layer, moreover, the excess hole-concentration or electron-concentration current quenches the excitons formed in the light emitting layer, so as to seriously decrease the efficiency and lifetime of the OLED device.
Fluorene sulfur oxide is a novel electron-lacked (i.e. hole type) compound and also a derivative of fluorene, which has a substituent of sulfone group (—SO2) at C-9. The sulfone group is an electron-withdrawing group, and has higher electron affinity and an energy band gap of approximately 2.8 eV; therefore, the fluorene sulfur oxide can easily conduct electrons for injection and transport. S atom in the sulfone group is at the highest valence state, so as the sulfone group can be a stronger antioxidant, thus the fluorene sulfur oxide has a strong thermal stability. These advantages of the fluorene sulfur oxide allow the fluorene sulfur oxide be a useful material for transporting electrons in the OLED device.
Due to star-shaped molecule structure, a compound of a star-shaped molecule structure has characteristics such as great molecular weight, large steric, high glass-transition temperature, poor crystallinity and easily forming a stable amorphous film. Currently, publicly used compounds have a star-shaped molecule structure, formed by a bridging unit, such as following compounds:
